During the setting up of production of an oil deposit, hydrocarbons flow in a duct, called a production column, from the bottom of the well up to the surface. At the bottom of the well, the pressure and temperature are relatively high, for example 100° C. and 300 bars. During the upward motion of the hydrocarbons towards the surface, these pressures and temperatures decrease with the result that the temperature at the outlet of the well is for example of the order of 30° C.
Thermal insulation of the well is particularly important since with it, it should be possible to ensure upward motion of the hydrocarbons recovered at the bottom of the well without the rheology of the hydrocarbons being notably modified. In particular, it is sought to maintain the temperature of the fluid at its fluidity temperature in order to avoid any problems of deposit and of plugging along the production column. These problems cause slowdowns in the production of hydrocarbons, including interruptions for intervention in the column, e.g. for scraping deposits. These delays in production generate rather considerable costs and should therefore be avoided as far as possible. Now, these production columns are installed in formations, the temperature of which may be very low. These low temperatures generally cause the setting of a certain number of hydrocarbon compounds, including paraffins in particular.
Moreover, when water is injected into the well, the intention may be to avoid its freezing or it may desired that it is not heated up by the soils of the formation which it crosses in order, for example, to maintain its weight and to cause certain favorable thermal phenomena, such as penetration of the deposit by embrittlement of the rock in regards to its thermal fracture. It may also be desired to avoid heat variations in the column upon stoppages of production that are likely to promote contractions of metal tubes or fracture of the cementation products.
Presently, thermal insulation and consolidation of the walls of a drill hole well are generally carried out by dual casing of the well, which consists of introducing two sets of stainless steel tubes placed concentrically as the well is gradually dug inside the formation. These concentric tubes form the casing sections of the production column. In a first phase, the tube touching the formation is cemented by injecting cement from the surface through the actual inside of the casing (the plugging method) or through drill rods (cementation currently designated by “inner string”). When a first so-called external tube is cemented to the formation, a second so-called internal tube with a smaller diameter is introduced and an insulating fluid is injected into the annular space formed by both of these concentric tubes. This insulating fluid has to gel or solidify in order to fill this space.
The first external tube has the main purpose of avoiding a caving-in of the walls of the well, of preventing inflows of water or gas into the drill hole, and of allowing the pressure and production of the well to be controlled; this is the casing of the well. With the second internal tube forming the casing, an annular space may be created in which a product or a mixture of products is placed, which is capable of thermally insulating the wall of the formation. Thus, any deterioration of the formation by heat transfer subsequent to the nearby passage of fluids with a high temperature as compared with that of the crossed formation is avoided whether the latter is in open air or under water. This annular space is generally filled from one of the ends of the duct, by pumping a liquid loaded with solid particles or by pumping a liquid gel.
Among the documents of the prior art, U.S. Pat. No. 4,258,791 describes a method for insulating a well that crosses very cold formations with a completion fluid introduced into the annular space described earlier. This fluid is then thickened in order to obtain the consistency of a grease by increasing the internal temperature of the drill hole duct, for a time determined to be required for this thickening. This completion fluid comprises a hydrocarbon oleaginous liquid phase resulting from oil refining, an aqueous phase, an oleophilic polymer of maleic anhydride and of a long-chain alpha-olefin, and a water-in-oil emulsifier. French Patent No. FR 2 741 420 describes a system for thermal and acoustic insulation of a duct of a well, which will become the production column. This system consists of an aerogel sleeve which surrounds the external tube over at least one portion of its length. The method for forming this sleeve comprises the steps for forming a liquid gel outside the well from a gel precursor and a liquid, replacing the liquid phase with a more volatile solvent promoting drying, and then removing the solvent contained in the gel in order to form the aerogel.
French Patent No. FR 2 774 009 and U.S. Pat. No. 4,438,072 propose installations for preparing and introducing the gel in the annular duct or as a sleeve around the casing or in the annular cavity. These preparation modes aim at modulating the nature of the gel depending on the depth and on the surrounding temperature of the casing. One of the important phases of these methods is not only mixing the products making up the gel, but rather causing gelling of the introduced compound at the suitable height and at the suitable time. This gelling is obtained by increasing the surrounding temperature of the gel, for example by injecting hot water or steam, or by injecting a more volatile solvent. The major difficulty is to be able to recover the introduced fluids by recycling the fluids in the column or by evaporation of the solvent. This is also the case in U.S. Pat. No. 4,296,814, which with the purposes of thermally insulating a drill hole well, proposes introducing through the end of the casing (external tube) either pierced or not with holes, a gelling composition between the tube and the crossed formation, and in a second step, introducing boiling water or steam in order to cause formation of the gel by a rise in temperature. The gels used in these documents are generally obtained from organometallic products in an aqueous solution or in an emulsion. However, it is customary to use pure polyurethane gels for filling the annular cavity of the production column either by depositing them on the outside of the casing, or by injecting them as an emulsion with water or in diluted form in a solvent. The risk is premature deposition of polyurethane particles formed on the walls of the tubes before arriving in the location in which the polymer should sediment or gel. Among the polyurethane gels used, U.S. Pat. No. 4,438,072 cites the mixtures of pre-polymers of polyisocyanate, in particular organic di-isocyanate with a diol or triol polyether such as glycerol or a glycol.
Moreover, in the more particular field of thermal insulation of ducts for transporting or transferring materials, patent WO 02/34809 describes the use of an insulating composition, as a gel of cross-linked polyurethane elastomer obtained by the reaction of polyol and polyisocyanate in the presence of an organic filler that is chemically inert towards isocyanates. In this document, the cited embodiments are the injection or pre-molding with the insulating composition in order to make thermally insulated, more or less flexible transfer ducts, which may be wound on reels, with perfect adhesion of the molded insulating material and a guaranteed seal of the assembly.
No application to the field of consolidation and insulation of oil drill wells is cited. Thus, in the field of oil drill wells, from all the techniques mentioned earlier, either difficulties arise for having the right mixtures arrive in the right locations, or difficulties arise for having the products sediment or gel at the right time, or for recovering the fluids required for these gel formations or sedimentations. Thus, the drill holes of the wells have many technical difficulties and many subsidiary implementation costs. These costs correspond to difficulties in handling these fluids, which decant, plug, or deposit where they should not, before reaching their final destination, in order to accomplish their final purpose which consists of fixing insulating tubings and/or casings of the production column.
From all the aforementioned techniques, it emerges that the major drawback is the duration for setting into place the drill hole well. Indeed, the times for drilling and consolidating a drill hole well are long since the progression of the drilling depends on the time required for tubing and casing each drilling section. It is only possible to pass on to the next section when the cementation and completion operations for each section over the whole of its casing length have been completed and this until the last drilled section is reached.
The object of the present invention is to provide a solution for finding a remedy to the major problem of the duration for setting into place a drill hole well. This solution also provides advantages in terms of improvement in the consolidation of the well, improvement in productivity, and in simplification of the implementation on location.